Infections with the human immunodeficiency virus (HIV-1) and hepatitis C virus (HCV) are among the most significant causes of human morbidity and mortality. Worldwide, there are more than 40 million (HIV-1) and 170 million (HCV) people infected with these viruses. In the United States, 0.6% (HIV-1) and 1.7% (HCV) of the population is infected. More than 25% of those infected with HIV are co-infected with HCV (up to 90% of i.v. drug users). Despite the success of highly active anti-retroviral therapy, there remains a need to develop additional drugs targeted to novel receptors that will ensure different susceptibilities to the development of resistance compared to protease and reverse transcriptase, the principal receptors of current drugs. In contrast, current therapies for HCV are wholly inadequate, and multiple first-generation drugs are needed. Resistance is quickly developed to drugs patterned after those effective against HIV-1. The genomes of both HIV-1 and HCV encode a viroporins, a small membrane protein with ion channel activity involved in the production of new virus particles in infected cells. We propose to take a structural approach to the design of drugs directed against these viroporins. This is technically challenging research because viroporins reside in cell membranes, and one of the most important things we have learned from our studies of membrane proteins is that they are distorted by membrane mimics, such as organic solvents and detergent micelles, and must be studies in their native phospholipid bilayer environment under physiological conditions. As part of this research we have developed a general NMR method for determining the structures of membrane proteins in phospholipid bilayers, and will apply it to these viroporins. Determining the native structures of Vpu (Virus protein u) from HIV-1 and the p7 protein from HCV are essential in order to understand the molecular mechanism of their biological activities and to accelerate the discovery of drugs that interfere with the activities that contribute to the infectivity of the virses. Because we express these proteins and domains of their cellular partners in bacteria, we have a great deal of flexibility in the design of experiments to characterize their interactions with both drugs and proteins.